Self-generated gas blast circuit interrupter embodying polyethylene



Patented July 18, 1950 SELF-GENERATED GAS BLAST CIRCUIT INTERRUPTER EMBODYING POLY- ETHYLENE Albert P. Strom, Pittsburgh, and Charles P. Hill,

Edgewood, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 6, 1947, Serial No. 784,332

4 Claims. (01. 175-30) This invention relates to circuit interrupter-s which generate arc-extinguishing and confining gases automatically upon the occurrence of an arc, relating particularly to devices embodying polyethylene as an arc-confining and extinguishing member.

While a great number of arc-confining and extinguishing materials have been employed in circuit interrupters, certain prior-art materials have been so outstanding in this service that they are often selected as a standard of comparison of materials. In particular, horn or vulcanized fiber and compressed boric acid have been accepted as a standard of comparison because they have exhibited generally desirable characteristics over a wide range of conditions of use.

It has been discovered that polyethylene has unusually good characteristics as a gas-generating material when exposed to arcs. Over a wide range of current, it has been found to be better than horn fiber, in most cases many 'times superior in the restored voltage to horn fiber. For certain applications, polyethylene has given results far better than those obtainable with boric acid. Consequently, polyethylene possesses certain unexpectedly superior characteristics to the best materials available to the art at the present time for use as an arc-extinguishing medium.

The object of this invention is to provide in a circuit interrupter an arc-confining and interrupting structure comprising polyethylene.

A further. object of the invention is to embody in a self-generated gas-blast circuit interrupter an arc-confining and interrupting structure comprising a body composed of at least 70% by weight of polyethylene of a molecular weight of from 10,000 to 40,000.

Other objects of the invention will in part be obvious, and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figure 1 is a vertical cross-section through a fuse;

Fig. 2 is a view in elevation, partly in section, of a self-expulsion type of lightning arres'ter; and

Fig. 3 is a graph plotting restored kilovolts against amperage for a number of materials including polyethylene.

According to the present invention, the arcconflning and arc-extinguishing gas-generating z portions of circuit interrupters are prepared from polyethylene. Polyethylene has been found to possess hitherto unknown properties far superior to any known material, at least within certain current ranges, when used in a circuit interrupter. Polyethylene is a hydrocarbon polymer having the following generic formula:

While a great variety of solid polymers of polyethylene are suitable for the practice of the invention, it is preferred to employ polyethylene polymers having an average molecular weight of from 10,000 to 40,000. In this range the higher molecular weight ethylene polymers tend to be horn hard and may be difllcult to process. Accordingly, there may be incorporated up to 30% by weight of resinous materials for softening or plasticizlng the polyethylene. Polyisobutylene of a molecular weight of 20,000 or more is a suitable material. Vinyl-type resins may be incorporated therein by milling. The polyethylene, alone or with plasticizing additions, may be extruded in the form of tapes, tubes, bars, and the like. In some cases, the extruded shapes, for example, tubes of ilve-eighths inch internal diameter, need only to be cut or sawed to length and are ready for use in fuse manufacture. The material may be readily machined to any predetermined shape.

As one application of polyethylene to a self gas-generating circuit interrupter, reference should be made to Figure l of the drawing, where there is illustrated a fuse l0 comprising a strain wire I! and a fusible wire it, both being connected to an upper terminal it which may be connected to one portion of a circuit passing through the fuse and a lower terminal ll connected by a flexible conductor 20 to a second terminal 22 which is connectible to complete the circuit. A tube "surrounding the strain and fuse wires l2 and II is prepared from polyethylene. If desired, only the inner portion of the tube 24 need be composed of polyethylene, and the outer portion may be composed of fiber, paper, or other suitable material. Upon a sufficiently high current passing through the wires l2 and It, they will fuse thereby creating an arc. The lower terminal is will drop, either because of the gas-pressure developed by the heat of the are alone, or, in some cases, by a spring (not shown) operating thereon, to draw the are out further. The heat of the arc will cause the polyethylene in the tube 24 to evolve gases which will cause extinction of the arc. It is believed that the gases produced by the action of the are on the polyethylene are lower polymers, and may even contain ethylene and hydrogen. The turbulent flow of these gases through the core of the arc rapidly cools and deionizes the arc, so that when the current reaches zero at the end of a half cycle, the arc will be extinguished without reforming.

Referring to Fig. 3 of the drawing, there are plotted curves of restored kilovolts against amperes, showing the interrupting ability of polyethylene in a iive-eighths inch by four-inch bore fuse. For comparative purposes, the curves for boric acid and fiber derived from a similar fuse are shown in the graph. The curves show interruption in five half-cycles or less for each of the materials. It will be noted that for from 40 amperes to approximately 400 amperes, polyethylene was superior in its ability to interrupt a higher voltage than either fiber or boric acid. Its interrupting ability reaches a peak of approximately two and a half times that of boric acid. Polyethylene is superior to fiber throughout the entire range of tests. Results obtained on testing one-quarter inch by four-inch bore fuses having polyethylene gas evolving liners indicated equally superior properties. The properties of polyethylene are so outstanding that fuses operating in the range of from 50 to 100 amperes may be made of approximately one-half the size now produced commercially, while giving equal interrupting results.

Polyethylene is a particularly desirable material for circuit interrupters because it is nonhygroscopic and therefore does not warp. It possesses extremely good electrical insulating properties, and for this reason also, its use is recommended in circuit interrupters. Being insoluble in water, polyethylene can be employed for applications in which other materials are not suitable. It possesses a considerable mechanical "strength and therefore will withstand the pressures developed by the generated gas on exposure to arcs, particularly in confined chambers.

A particularly desirable use for polyethylene is in self-expulsion type lightning arresters, one

form of which is'shown in Fig. 2 of the drawing.

The lightning arrester 30 comprises an exterior casing 32 preferably of porcelain, to which is ainxed an external contact member 34 which is connected to a power line or the like to be protected against lightning. An external gap is arranged between an arcin tip 36 and a cap 38 is ailixed to one end of the casing 32. The cap 33 extends inside of the casing 32, and terminates in an arcing contact 40 disposed inside of a sleeve 42 composed of polyethylene. At the lower end of the sleeve 02, there is located, in threaded engage'ment therewith, a hollow contact 44 forming an internal gap with respect to the arcing contact 4'. between which an arc is adapted to be drawn upon a lightning surge passing to the arrester 30. The hollow contact 44 is adapted to be grounded through the terminal 48. A slot 46 through the contact permits the expulsion of gases through the hollow contact 44 from the interior of the sleeve 42. The distance and arrangement oi the external gap 36-38 in series.

with the gap between contacts 40 and 44 is predetermined and requires a surge of a given value to be present at 34 before the lightning arrester will operate. When a lightning surge of this given value or greater is imposed on the contact internally between contacts 40 and II. The intemal arc will cause the polyethylene sleeve 42 to produce a volume of gas, and the deionizing effect-of the gas in conjunction'with the gas-blast effect will tend to blow the arc out and thereafter restore the electrical resistance of the lightning arrester proper. The gases produced during the arc-interrupting operation will be expelled through the slot 46 to the exterior of the arrester.

It will be appreciated that other forms of circuit interrupter may be constructed embodying polyethylene as an arc-confining and extinguishing material, since the above description and embodiments of the invention are illustrative and not limited.

We claim as our invention:

1. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed, and arc-confining and extinguishing means disposed along the path of the arc from which an arc-extinguishing gas can be evolved by the heat of the arc, the arc-confining and extinguishing means comprising a body composed of at least 70% by weight of polyethylene of an average molecular weight of from 10,000 to 40,000.

2. An electric circuit interrupter comprising, in combination, a pair of contact members disposed to produce an arc to interrupt a circuit established between them, a chamber within which the contact members are arranged, and arc-confining and extinguishing means disposed along the path of the are from which an arc-extinguishing gas can be evolved by the heat of an arc, the arcconfining and extinguishing means comprising a body composed of at least 70% by weight of polyethylene of an average molecular weight of from 10,000 to 40,000.

4. In a lightning arrester, in combination, means adapted to form an are when an electrical circuit embodying the arrester is struck by lightning, and an arc-confining and extinguishing means disposed along the path of the are from which an arc-extinguishing gas can be evolved by the heat of an arc, the arc-confining and extinguishing means comprising a body composed of at least 70% by weight of polyethylene of an average molecular weight of from 10,000 to 40,000.

ALBERT P. STROM. CHARLES F. HILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,157,832 Nowak et al. May 9, 1939 2,188,806 Burmeister Jan. 30, 1 940 2,328,825 McMahon Sept. 7, 1943 

